This invention relates to dishwashing machines and, more particularly to such machines incorporating a first pump and drive motor to recirculate fluid for washing articles in the machine and a separate pump and drive motor arranged to essentially completely discharge the wash fluid to drain and concurrently discharge accumulated soil particles to drain.
Typical domestic dishwashers in use today draw fluid from a sump at the bottom of the wash chamber and spray the fluid through various mechanisms in the wash chamber to wash soil from articles located in the chamber. Many such dishwashing machines include filter mechanisms to remove soil particles from the recirculated fluid. One such filter arrangement is disclosed in U.S. Pat. No. 3,807,419, which is incorporated herein by reference.
Normally, at the end of a wash or rinse cycle, much of the fluid in the washing machine is exhausted to a drain. However, prior art machines have not been of optimal design and operation as regards the drain operation. In many machines the arrangement of the sump, the recirculation pump and the drain pump is such that a significant residue of fluid remains in the sump and recirculation pump when the drain operation is complete. U.S. Pat. No. 3,810,480 discloses a dishwashing machine which uses a recirculation pump and a drain pump driven by a common motor to provide substantially complete draining of the sump. However, as the recirculation pump needs significantly more power than the drain pump, such an arrangement involves less than optimum usage of electric power, particularly during drain operations. Furthermore it depends upon operation of the drain pump, in its reverse direction, to prevent any fluid from being drawn back into the machine from the drain.
Prior art machines which filter soil particles from the recirculated fluid, normally discharge the accumulated soil particles through the drain pump. This is not the most effective arrangement as it requires that the drain pump cavity and blades be large enough to pass the largest soil particles. In addition, such operations often leave some soil particles in areas of the machine, like the sump for example, that can adversely effect the next operation of the machine.
It is an object of the present invention to provide a dishwashing apparatus which provides for substantially complete evacuation of the wash chamber and sump in an energy efficient manner and with a mechanism which effectively uses the available space.
It is another object of this invention to provide such an improved apparatus in which accumulated soil particles are prevented from returning to the recirculated fluid in a subsequent operation.
It is yet another object of this invention to provide such an improved dishwashing apparatus in which fluid being drained from the machine carries accumulated soil particles to drain without the particles moving through the drain pump mechanism.